In visual measurement methods based on a recognized technique which methods have been designed for measuring the physiological potential difference in the retina of the eye (ERG, electroretinogram) for visual stimulus on test animals the electrode types referred to and to be adjusted in the eye and which electrodes registrate the ERG response have been constructed such that the use of those requires anaesthesia or immobility of the test animal such that the contact part of the electrodes measuring the biopotential is well kept on place and that they could in such way measure ERG responses of the same size and without interference. For example, the thread electrode, the cotton wick-Ag/AgCl-electrode and a contact lens with golden coat-electrode described in publication Documenta Ophthalmologica 98: 2000, Bayer A. U., Mittag T., Cook P., Brodie S. E., Podos S. M. and Maag K-P. “Comparisons of the amplitude size and the reproducibility of three different electrodes to record the corneal flash electroretinogram in rodents”, p. 233-246, and penlike pointer tip including a light source for stimulation of the retina and the electrode blades for measuring the ERG response described in SU-patent publication 1648336 are these kind of recognized electrode types adjustable on the cornea of the eye.
On the other hand, also other recognized electrodes which have been designed for measuring the ERG response on a human, but which, in some cases, may be applied for monitoring test animals are designed by shape such that their use requires the subject to be immovable during the measurements. Electrodes described in these methods are:    (1) A looplike, so called, HK-loop electrode for clinical ERG-measurements (Documenta Ophthalmologica 81:1992, Hawlina M. and Konec B. “New noncorneal HK-loop electrode for clinical electroretinography”, p. 253-259; U.S. Pat. No. 5,154,174)    (2) A cluster of electrodes placed on the sclerotic membrane of eye, in which electrode cluster there are several separate contact blades of electrodes sank in a ringlike and concave insulation frame following the surface of the eye for use in clinical and experimental (that is for test animals) ERG measurements (U.S. Pat. No. 4,874,237).    (3) A contact lens kind of device placed on the corneal membrane of the eye for clinical monitoring of functioning of the cardiovascular system and ERG (U.S. Pat. No. 5,297,554).    (4) A nylon fibre electrode coated with silver and adjustable on the corneal membrane of the eye for clinical ERG registrations (U.S. Pat. No. 4,417,581).    (5) A thin, membrane-type, mold to desired form electrode including water to be attached on the corneal membrane for applying in clinical and experimental ERG measurements (U.S. Pat. No. 4,735,207).    (6) An electroretinografic transparent coat with taps holding the eyelids open to be adjusted on the corneal membrane for applying in clinical and experimental ERG measurements (FR patent publication 2713913).    (7) A metal strip to be attached on the skin, on the lower eyelid for example, which metal strip has been connected to a flexible plastic strip for measuring ERG and the outside cranium-reflected responses on a human (U.S. Pat. No. 4,255,023).    (8) A transparent cup electrode to be attached on the corneal membrane, on the edges of which cup electrode there is a metal ring for defining ERG on a human (U.S. Pat. No. 4,131,113).    (9) A metal wire to be attached on the lower eyelid on the skin for clinical ERG registrations (U.S. Pat. No. 5,506,633).
Most of these referred techniques enable the registration of ERG and other visual responses reflected outside the cranium on a conscious human, because a test person is able to stay immovable deliberately. Applying above mentioned techniques in monitoring test animals is difficult in that with registration of ERG on test animals under anaesthesia or made immovable the kind of drugs have to be used which change the functioning of cells of the central nerve system and thus the normal physiology of seeing.
The common limiting factor of recognized detectors designed for visual monitoring is their shape which may cause irritation changes in the eye or in the surrounding tissue or excessive stress on the eye if they were implanted permanently on the eye, for example under the eyelid. Secondly, a limiting factor, which excludes their permanent implantation in the eye is the fact that the electrode conductors have been described to be directed outwards from the eye where they have been presented to be connected to the actual measuring system. The third problem connected with recognized electrode detectors is the fact how the contact part measuring the biopotential and being connected to the tissue is kept on place while changing stresses are directed to it through the eye and the tissue around it. On the other hand, a problem connected with earlier mentioned is the fact that no stresses ought to be directed to the contact part of the electrode due to possible movements of the measuring wire.
The object of the invention is to eliminate these problems and to provide an electrode detector, which is (a) such by construction that the contact electrode part measuring the biopotential is fixed to hold on desired place, (b) the contact electrode part yields under mechanical stress directed to it and returns to its place by a little movement, (c) the electrode detector does not cause mechanical or chemical tissue injury and (d) mechanical stresses of the measuring wire which is possible to be connected to the electrode detector are not transmitted to the contact electrode part.